Professor Dumbledore is helping Harry destroy the Horcruxes. He went to Gaunt Shack as he suspected a Horcrux to be present there. He saw Marvolo Gaunt's Ring and identified it as a Horcrux. Although he destroyed it, he is still affected by its curse. Professor Snape is helping Dumbledore remove the curse. For this, he wants to give Dumbledore exactly x drops of the potion he made.
Value of x is calculated as maximum of p·ai + q·aj + r·ak for given p, q, r and array a1, a2, ... an such that 1 ≤ i ≤ j ≤ k ≤ n. Help Snape find the value of x. Do note that the value of x may be negative.
First line of input contains 4 integers n, p, q, r ( - 109 ≤ p, q, r ≤ 109, 1 ≤ n ≤ 105).
Next line of input contains n space separated integers a1, a2, ... an ( - 109 ≤ ai ≤ 109).
Output a single integer the maximum value of p·ai + q·aj + r·ak that can be obtained provided 1 ≤ i ≤ j ≤ k ≤ n.
5 1 2 3 1 2 3 4 5
30
5 1 2 -3 -1 -2 -3 -4 -5
12
In the first sample case, we can take i = j = k = 5, thus making the answer as 1·5 + 2·5 + 3·5 = 30.
In second sample case, selecting i = j = 1 and k = 5 gives the answer 12.
思路:首先对于每一个位置先用第一个数×一下,表示每一个数都有可能是起始位置,并且维护一个max数组,max【i】表示1-【i】的最大值
然后挑选第二个数字,算出来+上最大值max【i】,并且维护最大值,跑三遍就输出max【n】就是答案,也不太好描述,看代码吧
#include<bits/stdc++.h>
using namespace std;
long long dp[100090][4];
long long maxx[100060];
int main()
{
long long n,val[4];
while(scanf("%lld%lld%lld%lld",&n,&val[1],&val[2],&val[3])!=EOF)
{
memset(maxx,-0x3f3f3f3f,sizeof(maxx));
for(int i=1; i<=n; i++)
{
scanf("%lld",&dp[i][0]);
}
for(int i=1; i<=3; i++)
{
for(int j=1; j<=n; j++)
{
if(i==1)
dp[j][i]=dp[j][0]*val[i];
else
dp[j][i]=dp[j][0]*val[i]+maxx[j];
maxx[j]=max(maxx[j-1],dp[j][i]);
}
}
printf("%lld\n",maxx[n]);
}
}